Python写的一个简单DNS服务器实例

@author: RobinTang
'''

import socketserver
import struct

# DNS Query
class SinDNSQuery:
def __init__(self, data):
i = 1
self.name = ''
while True:
d = data[i]
if d == 0:
break;
if d < 32:
self.name = self.name + '.'
else:
self.name = self.name + chr(d)
i = i + 1
self.querybytes = data[0:i + 1]
(self.type, self.classify) = struct.unpack('>HH', data[i + 1:i + 5])
self.len = i + 5
def getbytes(self):
return self.querybytes + struct.pack('>HH', self.type, self.classify)

# DNS Answer RRS
# this class is also can be use as Authority RRS or Additional RRS
class SinDNSAnswer:
def __init__(self, ip):
self.name = 49164
self.type = 1
self.classify = 1
self.timetolive = 190
self.datalength = 4
self.ip = ip
def getbytes(self):
res = struct.pack('>HHHLH', self.name, self.type, self.classify, self.timetolive, self.datalength)
s = self.ip.split('.')
res = res + struct.pack('BBBB', int(s[0]), int(s[1]), int(s[2]), int(s[3]))
return res

# DNS frame
# must initialized by a DNS query frame
class SinDNSFrame:
def __init__(self, data):
(self.id, self.flags, self.quests, self.answers, self.author, self.addition) = struct.unpack('>HHHHHH', data[0:12])
self.query = SinDNSQuery(data[12:])
def getname(self):
return self.query.name
def setip(self, ip):
self.answer = SinDNSAnswer(ip)
self.answers = 1
self.flags = 33152
def getbytes(self):
res = struct.pack('>HHHHHH', self.id, self.flags, self.quests, self.answers, self.author, self.addition)
res = res + self.query.getbytes()
if self.answers != 0:
res = res + self.answer.getbytes()
return res
# A UDPHandler to handle DNS query
class SinDNSUDPHandler(socketserver.BaseRequestHandler):
def handle(self):
data = self.request[0].strip()
dns = SinDNSFrame(data)
socket = self.request[1]
namemap = SinDNSServer.namemap
if(dns.query.type==1):
# If this is query a A record, then response it

name = dns.getname();
if namemap.__contains__(name):
# If have record, response it
dns.setip(namemap[name])
socket.sendto(dns.getbytes(), self.client_address)
elif namemap.__contains__('*'):
# Response default address
dns.setip(namemap['*'])
socket.sendto(dns.getbytes(), self.client_address)
else:
# ignore it
socket.sendto(data, self.client_address)
else:
# If this is not query a A record, ignore it
socket.sendto(data, self.client_address)

# DNS Server
# It only support A record query
# user it, U can create a simple DNS server
class SinDNSServer:
def __init__(self, port=53):
SinDNSServer.namemap = {}
self.port = port
def addname(self, name, ip):
SinDNSServer.namemap[name] = ip
def start(self):
HOST, PORT = "0.0.0.0", self.port
server = socketserver.UDPServer((HOST, PORT), SinDNSUDPHandler)
server.serve_forever()

# Now, test it
if __name__ == "__main__":
sev = SinDNSServer()
sev.addname('www.aa.com', '192.168.0.1') # add a A record
sev.addname('www.bb.com', '192.168.0.2') # add a A record
sev.addname('*', '0.0.0.0') # default address
sev.start() # start DNS server

# Now, U can use "nslookup" command to test it
# Such as "nslookup www.aa.com"